rspec_examples.md

RSpec Examples

Without Always Execute

Notice in the test below there is setup, execute, and assert code all in the it blocks. Different test cases are not separated by contexts, instead they're all just strewn together; it may not be immediately obvious, but we're really testing 3 different cases below (not 4 - the first 2 its describe the default behavior of the dvd_player). It's easy to see how these problems could be much worse given a less trivial example and how these tests would not serve as the best documentation of how dvd_player#play works.

describe DvdPlayer do
  before do
    @dvd_player = DvdPlayer.new
    @dvd = Dvd.new
  end

  it "should play movie" do
    @dvd_player.play(@dvd)
    @dvd_player.movie_playing?.should be_true
  end

  it "should not allow another disc to be inserted" do
    @dvd_player.play(@dvd)
    @dvd_player.allows_disc_insert?.should be_false
  end

  it "should not play movie with invalid region code" do
    @dvd.region_code = 'invalid'
    @dvd_player.play(@dvd)
    @dvd_player.movie_playing?.should be_false
  end

  it "should resume from last played postiion with previously played dvd" do
    @dvd.last_played_position = 123
    @dvd_player.play(@dvd)
    @dvd_player.movie_playing?.should be_true
    @dvd_player.current_position.should == 123
  end
end

With Always Execute

When using always execute, you'll notice it's a lot DRYer, but more importantly all the setup, execute, and assert code is cleanly separated. Furthermore, test cases are cleanly separated by contexts. This makes it much easier to see that the first two should blocks apply to the default case, whereas the following contexts apply to exception cases. It's also much easier to see what makes the exception cases different, since their setup code is cleanly spelled out, rather than lumped in with other code.

describe DvdPlayer do
  describe "#play" do
    before do
      @dvd_player = DvdPlayer.new
      @dvd = Dvd.new
    end

    execute do
      @dvd_player.play(@dvd)
    end


    it "should play movie" do
      @dvd_player.movie_playing?.should be_true
    end
  
    it "should not allow another disc to be inserted" do
      @dvd_player.allows_disc_insert?.should be_false
    end

    context "with invalid region code" do
      before do
        @dvd.region_code = 'invalid'
      end

      it "should not play movie" do
        @dvd_player.movie_playing?.should be_false
      end
    end

    context "with previously played dvd" do
      before do
        @dvd.last_played_position = 123
      end

      it "should resume from last played position" do
        @dvd_player.movie_playing?.should be_true
        @dvd_player.current_position.should == 123
      end
    end    
  end
end

Other Features

execute_result

Often in specs, you are testing the returned value of a single function. For connivence, the returned value of an execute block is stored in a variable called @execute_result.

describe DvdPlayer do
  describe "#current_dvd" do
    before do
      @dvd_player = DvdPlayer.new
    end

    execute do
      @dvd_player.current_dvd
    end

    context "without any dvd in the player" do
      it "should return no dvd" do
        @execute_result.should be_nil
      end
    end

    context "with a dvd in the player" do
      before do
        @dvd = Dvd.new
        @dvd_player.insert(@dvd)
      end

      it "should return the dvd in the player" do
        @execute_result.should == @dvd
      end
    end
  end
end